Fluorocarbon based fluids have found widespread use in many commercial and industrial applications, including as aerosol propellants and as blowing agents. Because of certain suspected environmental problems, including the relatively high global warming potentials, associated with the use of some of the compositions that have heretofore been used in these applications, it has become increasingly desirable to use fluids having low or even zero ozone depletion potential, such as hydrofluorocarbons (“HFCs”). Thus, the use of fluids that do not contain substantial amounts of chlorofluorocarbons (“CFCs”) or hydrochlorofluorocarbons (“HCFCs”) is desirable. Furthermore, some HFC fluids may have relatively high global warming potentials associated therewith, and it is desirable to use hydrofluorocarbon or other fluorinated fluids having as low global warming potentials as possible while maintaining the desired performance in use properties.
As suggested above, concern has been increasing in recent years about potential damage to the earth's atmosphere and climate, and certain chlorine-based compounds have been identified as particularly problematic in this regard. The use of chlorine-containing compositions (such as chlorofluorocarbons (CFC's), hydrochlorofluorocarbons (HCF's) and the like) in many applications has become disfavored because of the ozone-depleting properties associated with many of such compounds. There has thus been an increasing need for new fluorocarbon and hydrofluorocarbon compounds and compositions that are attractive alternatives to the compositions heretofore used in these and other applications. For example, it has become desirable to retrofit chlorine-containing systems, such as blowing agent systems or refrigeration systems, by replacing chlorine-containing compounds with non-chlorine-containing compounds that will not deplete the ozone layer, such as hydrofluorocarbons (HFC's). Industry in general is continually seeking new fluorocarbon based mixtures that offer alternatives to, and are considered environmentally safer substitutes for, CFCs and HCFCs. It is considered important in many cases, however, that any potential substitute must also possess those properties present in many of the most widely used fluids, such as imparting excellent thermal insulating properties and other desirable foam characteristics when used as blowing agents, such as appropriate chemical stability, low- or no-toxicity, low or no-flammability, among others.
Furthermore, it is generally considered desirably for CFC blowing agent substitutes to be effective without major engineering changes to conventional foam generating systems.
Methods and compositions for making conventional foamed materials, such as for example thermoplastic materials and thermosetting materials, have long been known. These methods and compositions have typically utilized chemical and/or physical blowing agents to form the foamed structure in a polymeric matrix. Such blowing agents have included, for example, azo compounds, various volatile organic compounds (VOCs) and chlorofluorocarbons (CFCs). The chemical blowing agents typically undergo some form of chemical change, including chemical reaction with the material that forms the polymer matrix (usually at a predetermined temperature/pressure) that causes the release of a gas, such as nitrogen, carbon dioxide, or carbon monoxide. One of the most frequently used chemical blowing agents is water. The physical blowing agents typically are dissolved in the polymer or polymer precursor material and then expand volumetrically (again at a predetermined temperature/pressure) to contribute to the formation of the foamed structure. Physical blowing agents are frequently used in connection with thermoplastic foams, although chemical blowing agents can be used in place of or in addition to physical blowing agents in connection with thermoplastic foam. For example, it is known to use chemical blowing agents in connection with the formation of polyvinylchloride-based foams. It is common to use chemical blowing and/or physical blowing agents in connection with thermosetting foams. Of course, it is possible that certain compounds and the compositions that contain them may at once constitute a chemical and a physical blowing agent.
It was common in the past that the CFCs were used as standard blowing agents in the preparation of isocyanate-based foams, such as rigid and flexible polyurethane and polyisocyanurate foams. For example, compositions consisting of CCl3F (CFC-11) had become a standard blowing agent. However, the use of this material has been banned by international treaty on the grounds that its release into the atmosphere damages the ozone layer in the stratosphere. As a consequence, it is no longer generally common that neat CFC-11 is used as a standard blowing agent for forming thermosetting foams, such as isocyanate-based foams and phenolic foams.
The problems with CFCs led to the more frequent utilization hydrogen-containing chlorofluoroalkanes (HCFCs). For example, CHCl2CF3 (HCFC-123) and CH2ClCHClF (HCFC-141b) have relatively short lifetimes in the atmosphere. However, while HCFCs are considered to be environmentally friendly blowing agents relative to CFCs, such compounds still contain some chlorine, and therefore have an “Ozone Depletion Potential” (called “ODP”). Because of the non-zero ODP, HCFCs, have been targeted for eventual removal from use.
Another known class of blowing agents is the non-chlorinated, partially hydrogenated fluorocarbons (called “HFCs”). Certain of the HFC currently being used as blowing agents have at least one potentially serious problem, namely that they generally have relatively high intrinsic thermal conductivity properties (i.e., poor thermal insulation). On the other hand, foams made with certain of the more modern HFC blowing agents, such as CF3CH2CF2H (“HFC-245fa”) offer improved thermal insulation, due in part to the low thermal conductivity of HFC-245fa vapor, and due in part to the fine cell structure HFC-245fa imparts to the foams. HFC-245fa has been widely used in insulation applications, particularly refrigerator, freezer, refrigerator/freezer and spray foam applications. Nevertheless, many HFC fluids share the disadvantage of having relatively high global warming potentials, and it is desirable to use hydrofluorocarbon or other fluorinated fluids having as low global warming potentials as possible while maintaining the desired performance in use properties. Even the more modern HFCs, such as HFC-245fa, HFC-134a, HFC-365mfc, and others, exhibit a higher than desirable global warming potential, albeit low relative to other HFCs. Thus, the use of HFCs as blowing agents in foam insulation, particularly rigid foam insulation, has resulted in HFCs being less desirable candidates for blowing agents in commercial foam insulation.
Hydrocarbon blowing agents are also known. For example, U.S. Pat. No. 5,182,309 to Hutzen teaches the use of iso- and normal-pentane in various emulsion mixtures. Another example of hydrocarbon blowing agents is cyclopentane, as taught by U.S. Pat. No. 5,096,933—Volkert. Although many hydrocarbon blowing agents, such as cyclopentane, and isomers of pentane, are zero ozone depleting agents and exhibit very low global warming potential, such material are less than fully desirable because foams produced from these blowing agents lack the same degree of thermal insulation efficiency as foams made with, for example, HFC-245fa blowing agent. Further, the hydrocarbon blowing agents are extremely flammable, which is undesirable. Also, certain hydrocarbon blowing agents have inadequate miscibility in certain situations with material from which the foam is formed, such as many of the polyester polyols commonly used in polyisocyanurate modified polyurethane foam. The use of these alkanes frequently requires a chemical surfactant to obtain a suitable mixture.
There has thus been an increasing need for new compounds and compositions that are attractive alternatives to the compositions heretofore used as blowing agents in these and other applications. Applicants have thus recognized a need for new fluorocarbon based compounds and compositions that offer effective alternatives to, and are considered environmentally safer substitutes for, CFCs and HCFCs. It is generally considered highly desirable, however, that any potential substitute must also possess properties, or impart properties to the foam, that are at least comparable to those associated with many of the most widely used blowing agents, such as vapor phase thermal conductivity (low k-factor), low- or no-toxicity, among others.
One such other potentially important property in many applications is flammability. That is, it is considered either important or essential in many applications, including particularly in blowing agent applications, to use compositions which are of low flammability or are non-flammable. As used herein, the term “nonflammable” refers to compounds or compositions which are determined to be nonflammable as determined in accordance with ASTM standard E-681, dated 2002, which is incorporated herein by reference. Unfortunately, many HFC's which might otherwise be desirable for used in foam blowing agent compositions are not nonflammable. For example, the fluoroalkane difluoroethane (HFC-152a) and the fluoroalkene 1,1,1-trifluorpropene (HFO-1243zf) are each flammable and therefore not viable for use in many applications.
Anther example of a relatively flammable material is the fluorinated ether 1,1,22-tetrafluoroethyl methyl ether (which is referred to as HFE-254pc or also sometimes as HFE-254cb), which has been measured to have a flammability limit (vol %) of from about 5.4% to about 24.4%. Fluorinated ethers of this general type have been disclosed for use as blowing agents in U.S. Pat. No. 5,137,932—Beheme et al, which is incorporated herein by reference.
It has been suggested to use bromine-containing halocarbon additives to decrease flammability of certain materials, including foam blowing agents, in U.S. Pat. No. 5,900,185—Tapscott. The additives in this patent are said to be characterized by high efficiency and short atmospheric lifetimes, that is, low ozone depletion potential (ODP) and a low global warming potential (GWP).
While the brominated olefins described in Tapscott may have some level of effectiveness as anti-flammability agents in connection with certain materials, there is no disclosure of the use of such materials as a blowing agent. Furthermore, it is believed that such compounds may also have certain disadvantages. For example, applicants have come to recognize that many of the compounds identified in Tapscott will have a relatively low efficiency as a blowing agent due to the relatively high molecular weight of such compounds. In addition, it is believed that many of the compounds disclosed in Tapscott will encounter problems when used as a blowing agent due to the relatively high boiling point of such compounds. Moreover, it is understood by applicants that many compounds which have a high level of substitution may possess undesirable toxicity properties and/or other undesirable properties, such as potentially environmentally undesirable bioaccumulation.
While Tapscott indicates that bromine-containing alkenes having from 2 to 6 carbon atoms may also contain fluorine substituents, this patent appears to suggest that fluorine-containing compounds are less than fully desirable from the standpoint of environmental safety by noting that “non-fluorine-containing bromoalkanes will have very short atmospheric lifetimes due to reaction with tropospheric hydroxyl free radicals.” (Col. 8, I. 34-39).
Furthermore, it is generally considered desirable for blowing agent substitutes to be effective without major engineering changes to conventional equipment and systems used in foam preparation and formation.
Applicants have thus come to appreciate a need for compositions, and particularly blowing agents, foamable compositions, foamed articles and methods and systems for forming foam, which provide beneficial properties and/or avoid one or more of the disadvantages noted above.
This invention relates to compositions, methods and systems having utility in numerous applications, including particularly in connection with compositions, methods, systems and agents relating to polymeric foams.